The effects of grain boundary misorientation on grain boundary segregation in 304 stainless steels

• Main Authors: Ting Shien Duh, 杜定賢
• Other Authors: Ji Jung Kai
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/04711259946051992086

博士 === 國立清華大學 === 工程與系統科學系 === 89 === The purpose of this study is to investigate the effects of the grain boundary misorientation on the radiation induced segregation (RIS) in 304 stainless steels. For the experiments, there were 4 test conditions for the specimens: (1) As-received (AR) with enriched Cr at grain boundary, (2) AR + 1dpa proton irradiation at 450oC, (3) Thermal sensitized (SEN), and (4) SEN + 1dpa proton irradiation at 450oC. The Cr/Ni concentration profiles were measured by using FEGTEM/EDS and the grain boundary misorientation was determined with the aid of simulated Kikuchi patterns. A delayed Cr depletion compared to no pre-enrichment condition was observed at grain boundaries in AR + 1dpa specimens. The Cr concentration profiles were found to be narrower and deeper in SEN + 1dpa specimens. The degree of grain boundary segregation was observed to be higher at random boundaries than special boundaries. The segregation cusps were measured at grain boundaries of S3, S9 and S15 in SEN + 1dpa 304 stainless steel specimens. From the fitted segregation cusps, it seems that the Cr segregation level at special boundaries in irradiated sensitized 304 stainless steels are increasing with S for value up to S = 21. For the model, a simple rate equation model with modified boundary conditions, which included the fluxes of defects diffusing along the grain boundaries to the grain boundary dislocations, was developed for RIS at boundaries with different S values. The results of the model calculations were compared to the experimental results and it was found that the model could clearly predict the same trends that the Cr depletion levels at special boundaries in irradiated 304 stainless steels were increasing with S.